This Standard specifies signalling interworking between "QSIG" and "H.323" in support of call diversion supplementary services within a Corporate telecommunication Network (CN).

"QSIG" is a signalling protocol that operates at the Q reference point between Private Integrated Services eXchanges (PINX) within a Private Integrated Services Network (PISN). The Q reference point is defined in ECMA-133. A PISN provides circuit-switched basic services and supplementary services to its users. QSIG is specified in other Ecma Standards, in particular ECMA-143 (call control in support of basic services), ECMA-165 (generic functional protocol for the support of supplementary services) and a number of standards specifying individual supplementary services. ECMA-174 specifies the QSIG protocol in support of call diversion services.

"H.323" is a set of signalling protocols for the support of voice or multimedia communication within a packet network, in particular a packet network that uses the Internet Protocol (IP) as its network layer protocol (IP network). H.323 signalling protocols operate between endpoints in an IP network, either indirectly via one or more gatekeepers, or directly. An endpoint can be a terminal or a gateway to another network. H.323 is an "umbrella" recommendation referring to various ITU-T recommendations, in particular Recommendations H.225.0 and H.245 (basic communication capabilities) and Recommendation H.450.1 (generic functional protocol for the support of supplementary services). Recommendation H.450.3 specifies the H.323 protocol in support of call diversion services.

NOTE H.450.3 applies only to the 1998 version of H.323 (also known as H.323 version 2) and to later versions.

This standard is applicable to any interworking unit that can act as a gateway between a PISN employing QSIG and an IP network employing H.323.